1. Field of the Invention
This invention relates to the use of prosthetic ball joint cups in the surgical procedures to replace skeletal joints such as a hip joint.
2. Description of Prior Art
During these procedures, it has been noted that any discontinuity in the rim or wall of the acetabulum of the innominate bone, for example the acetabular notch between the transverse ligament, is instrumental in causing problems where the fixing bone cement used to bond the ball joint cup to the surface of the acetabulum is often lost through the discontinuity. In order to prevent this loss of cement, a fixing plate is placed inside the acetabulum, blocking the discontinuity and allowing the ball joint cup to be pushed into place without loss of cement.
According to the present invention, a prosthetic acetabulum fixing plate comprises a component to be located into the acetabulum prior to the insertion of a prosthetic ball joint cap. The plate has a closure wall adapted to close the wall or rim of the acetabulum across any discontinuity therein, and a locator element is provided for locating the closure wall in place.
The fixing plate can be supplied in various sizes and arrangements, the correct plate being chosen by the surgeon after close examination of X-ray photographs of the patient and through the use of a template which is used to determine the size and arrangement of the discontinuity and thus the correct size and arrangement of the plate to be used.
The plate can be made from any suitable material but is preferably made from a synthetic plastic material for example polymethylmethacrylate, (P.M.M.A.). Preferably the fixing plate also has a lining portion adapted to extend across the depressed portion of the acetabulum (the fossa). This lining portion can have apertures to enable fixing cement to extend through it.
The plate can be used after a filling material such as bone graft is used to fill the depression in the inner surface of the acetabulum, the acetabular component then being placed over the filling material. The plate can then become a continuation of the substantially continuously circular nature of the outer rim of the acetabulum.
The surface of the closure wall can be adapted to include a location and depth defining element adapted for use in conjunction with an acetabular cup with a disposable flange or a fixed flange or indeed without a flange if the closure wall is adapted to engage the appropriate portion of the cup, so that location and depth defining means are provided for the acetabular cup.
The apertures in the plate face can be of a size consistent with the passage of the fixing cement used to bond a prosthetic ball joint cup into the acetabulum. The plate can be dimensioned in varying size dependent on the patient. The device for locating the plate and closure wall in position may conveniently comprise a clip adapted to extend over the rim of the acetabulum adjacent to any discontinuity.